Heretofore the fillers in dental composites have been composed of particles from about 0.56 micron to about 150 microns in diameter. These relatively large particles have resulted in a rougher type of finish than many practitioners desired. Yet, although some manufacturers used a small amount of submicron filler particles, which are typically 0.02 to 0.04 micron in diameter (to eliminate settling, for example), they have used them only up to about 5% by weight of the composite, and most of the particles remained relatively large.
Recently, various manufacturers have placed on the market "microfilled" composites in which all of the filler was in the 0.02 to 0.04 micron range, and a smoother finish was thereby obtained. However, when using these small particle fillers, only about 25% to 50% of the composite could be filler.
When such a relatively small percentage of filler was added to the typical dental resin, the result was that physical properties, such as tensile strength and water sorption, were severely compromised.